題目：

對于一棵二叉樹，請設(shè)計一個算法，創(chuàng)建含有某一深度上所有結(jié)點的鏈表。

給定二叉樹的根結(jié)點指針TreeNode* root，以及鏈表上結(jié)點的深度，請返回一個鏈表ListNode，代表該深度上所有結(jié)點的值，請按樹上從左往右的順序鏈接，保證深度不超過樹的高度，樹上結(jié)點的值為非負(fù)整數(shù)且不超過100000。

思路：
每次往下一層，dep-1

# -*- coding:utf-8 -*-
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class TreeLevel:
    l = ListNode(-1)
    p = l
    def getTreeLevel(self, root, dep):
        # write code here
        if not root or dep == 0:
            return
        if dep == 1:
            self.p.next = ListNode(root.val)
            self.p = self.p.next
        else:
            self.getTreeLevel(root.left,dep-1)
            self.getTreeLevel(root.right,dep-1)
        return self.l.next

if __name__ == '__main__':
    head = TreeNode(1)
    head.left = TreeNode(2)
    head.right = TreeNode(3)

    head.left.left = TreeNode(4)
    head.left.right = TreeNode(5)

    head.left.left.left = TreeNode(6)
    head.left.left.right = TreeNode(7)

    s = TreeLevel()
    s.getTreeLevel(head,2)
    print(s.l.next.val)